A512

Memory Expansion for Amiga 500(+)

The A512 is a new interpretation of a 512K trapdoor memory expansion for the
Amiga 500 computer. This means that it's not just yet another copy of a product
that was available from lots of second-source manufacturers during the late
1980s and 1990s, but it is taking care of today's A500 users' needs:

Today's collectors and computer restauration experts like to keep a separate
computer with a full OCS chipset and just a trapdoor memory expansion for the
classic 0.5M ChipMem and 0.5M RangerMem configuration. With many second-source
memory expansions using megabit memory chips, the setup will tend to run unstable,
because the OCS Agnus types 8370 and 8371 will not generate enough refresh
addresses for most trapdoor memory expansions that use less than 16 memory chips.

The A512 memory expansion will run properly with all Agnus types, including OCS chips.
Thanks to an additional refresh circuit, the single 4Mbit memory chip will get
enough refresh addresses to keep its contents in any configuration.

When operated in an A500+ computer, the A512 will be used as ChipMem, and two of
these expansions can be cascaded to reach the maximum configuration of 2 MBytes
of graphics memory (1 MByte on the main board and 1 MByte in the trapdoor
slot). The pass-through port is compatible with any other 512K trapdoor expansion
as long as it fits mechanically. The A500+ on-board RTC is only switched off if
the RTC module has been installed on the A512 card.

The A512 memory expansion is compatible with all motherboard revisions
from Rev. 3 to Rev. 8, including the A500+.